Re: [filter-effects] Color clamping of intermediate filter primitive results

On Mon, Jul 22, 2013 at 10:16 PM, Dirk Schulze <dschulze@adobe.com> wrote:

> Hi,
>
> Currently Filter Effect require to clamp all resulting pixel color values
> of filter primitives to the range 0..255. This was done to have specified
> color values for each filter primitive output at any time.
>
> However, this approach prevents implementations from further improvements.
> The specification currently has the following note for shorthand filters[1]:
>
> ""
> Note: The grayscale, sepia, saturate, hue-rotate, invert, opacity,
> brightness and contrast filter functions can be represented by color
> matrices. If the former named filter functions are chained together, UAs
> can optimize the performance by multiplying these filter functions to one
> color matrix and apply the resulting color matrix instead of each filter
> function separately.
> ""
>

I think you should remove that sentence or make it clear that clamping
needs to be done when you collapse the matrices.


>
> Since the shorthand filter build on top of SVG Filters, this is actually
> not correct. Implementations need to apply each shorthand filter on the
> content first to clamp the result after each filter operation.
>
> "saturate(200%) saturate(50%)" would look different depending if you clamp
> color values for each primitive or don't.
>
> I wonder if we can relax the requirement of clamping in some cases and
> would suggest that we do not force clamping if two following filter
> primitives can be collapsed to one filter primitive. We would need to
> clarify which primitives can be combined together of course.
>
> Greetings,
> Dirk
>
> [1] http://dev.w3.org/fxtf/filters/#FilterProperty
>
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